Insulating shield for cathode-ray tubes



y 1, 1952 R. A. FISCH 2,602,112

INSULATING SHIELD FOR CATHODE-RAY TUBES Filed July 12, 1949 J5EE. BY 2 Mm JITTORNEZY Patented July 1, 1952 "UNITED STATES PATENT OFFICE INSULATING SHIELD FOR CATHODE-RAY TUBES Richard A. Fisch, Kew Gardens, N. Y.

Application July 12, 1949, Serial No. 104,289

V Claims. 1

This'invention relates to a novel device for shielding and protecting a metal backed television or cathode ray tube, more particularly it relates to a novel means for attaching an insulating shield tosuch' a tube.

This application is a continuation-in-part of application No. 73,058, filed January 27, 1949, now PatentNo. 2,503,813.

The general idea of shielding electrical equipment having exposed parts is old and well known but the shielding of metal backed cathode ray or television tubes presents peculiar diificulties. Themetal backed cathode ray or television tubes comprise a glass bulb containing the electrode structure, a metal tube section which has a varying diameter (usually frustoconical) the small end of which is united to the end of the glass bulb and a glass lens element which is united to the open or largeend of the said metal tube. In order that a good seal can be obtained between thelens and the metal backing; the metal back or conical section is flared outwardly at the large end to form aseat for the round edge portion of the lens. Itis important to have a shield which fits closely about the metal backing and which also fits over the fiaredportion of the tube since thisflared portion is the part which is most likely to be contacted. When a conical shield is placed about the tube it has a tendency to slip backward, away from the flared end or lens containing end of the tube, especially if the conical shield is made large enough to fit about the flared end of the metal backing. The metal back of such a tube is ordinarily placed under a voltage of 14,000 to 19,000 volts by What is called the second anode connection.

An object of this invention therefore is to provide an improved insulating guard or shieldfor a metal backed cathode ray tube together with a means for holding the shield inplace about the tube. p

Another object of the invention is to provide an improved insulating shield for a'metal backed cathode ray or television tube provided with means for applying the second anode connection to the metal backing.

Another object of the invention is to provide an improved means for securing an insulating shield to a cathode ray or television tube.

Another object of the invention is to provide an improved ring of insulating material adapted to hold a shield in place on a television tube.

'I'heseobjects and others ancillary thereto are obtained by making a conical shield fromplastic material having a high insulating value which may be relatively stiff but is still bendable. The outer edge of the conical shield or skirt may ,contain loops or be otherwise formed so that the outer edge can be fitted about and held on the flared portion of the tube and a circular clamping member made of flexible insulating material is provided to securely hold the large portion of the skirt or shield snugly about the flared 'por tion of the tube. Preferably the circular 'clamping member has the cross sectional shape of a distorted H and .two of the legs of the H fit about the flange while the other two legs of the H extend away from theflanged edge and are adapted to hold an elastic member which in turn holds the clamping member tightly about the flanged edge of the tube. The outside groove of the clamping member which holds the elastic member also may be made deep enough'to hold the edge of the cabinet structurewhich contains the opening for the television tube. l

The ring must fit snugly about the flared end of the tube and therefore must be .open at one area to permit the inside groove to straddle the flared flange of the tube. It is difiicult to make the ring with such precision that it fits together at the cut portion after being inserted on the flange especially since the flanges of th tubes vary considerably. Since the metal back isunder such a high voltage any small almost insignificant opening or break in the-insulating ringis enough to permit a spark or static charge to seek a ground and severely shock any person or animal who approaches too close to the uninsulated area. Small pieces of insulating material may be placed inside of the opening in the ring but this expedient does not have the approval of the Underwriters Laboratories because such pieces are easily lost or misplaced when a television set is being repaired and there is no assurance that they would be replaced. The ring made according to this invention has anintegral flap on one end of the openringadaptedto-fit under the other end of the ring so that every portion of the flange of the television tube must always be covered by insulating material. V In general any resinous plastic material which has insulating properties may be employed to make the shield of the present invention. The shield may be formed from a flat sheet of material by first cutting to the shape of an appropriate sector and then uniting the edges to form a frustoconical tube. The edges may be united in any desired way as by-heat sealing, cementing or by providing interfitting parts on the edges to be united. The hydrocarbon polymeric materials such as polyethylene, polyisobutylene, polystyrene, polymers and copolymers of butadienes, polymers and copolymers of methyl substituted homologues of butadiene such as isoprene, etc. are very suitable as the material for the shield. Other polymeric materials having high insulating values which may be employed are the polymers and copolymers of vinylidene chloride and vinyl fluoride, polyvinyl carbazole, polyvinyl naphthalene, etc. Impregnated fabrics such as cellulose acetate impregnated with vinyl :butyral and similar materials may also be employed. 7

The clamping member is made from the same type of material as the shield and may be formed by an extrusion process, by an injection molding process or by any other molding process. When formed by extrusion it is necessary to mold the thin flap portion after the extruded strip is formed and cut to shape.

In order to apply a voltage to the metal backing, a metal strip adapted to extend inwardly from the large end and on the inside of the shield and having a conductor at one end thereof which extends through the shield is provided. The metal strip is held against the metal backing by clamping member. The outside portion of the conductor is attached to one part of a metal snap button device and the other part of the snap button is adapted to be soldered to a connecting wire so that the wire can be soldered to one part of the snap button without melting the insulating shield.

The novel features characteristic of this invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operating, together with additional objects and advantages thereof, will best be understood from the following description of specific embodiments when read in connection with the accompanying drawings in which:

Figure '1 is a top plan view of a television tube with the shield of the present invention attached thereto.

Figure 2 is a plan view of a retaining ring made i according to the invention.

Figure 3 is a detail view taken on line 33 of Figure 1 showing how the end of the ring overlaps.

Figure 4 is a detail view of the separated ends of the ring.

Figure 5 is a side cross sectional view showing one method of forming the flap end of the ring.

Figure 6 is a cross sectional view of the mold of Figure 5 along line 6--6 of Figure 5. s

Figure '7 is a perspective view showing a modified form of the conical portion of the device.

Figure 8 is a detail front view of the second anode connecting means. 7

Figure 9 is a detail side view of the second anode connecting means with the snap portions separated.

The television tube for which this invention is specially useful is shown in Figure 1 and comprises the socket IG, the glass bulb section II containing the electrode, the metal backing I3 and the lens I l. The metal backing I3 is united to the glass bulb II at I2 and is flared at I5 to provide a seat for the glass lens element I4. The conical skirt or shield 20 is adapted to extend from the flare I5 back over a considerable portion of the metal part l3 of the tube although it can be considerably shorter than shown if no 4 parts of the set approach close to the narrow end of the metal back I3.

The skirt or conical shield portion 23 may be slit at the edge of the wide end as shown at 25 to permit the edge portion to flare out and follow the contour of the metal backing. These flared portions formed by slits 25 are firmly held by the ring 36 to be described below. As shown in Figure 7 the skirt 20 may also be held on ring 39 by passing the ring through integrally formed loops 38. The loops are merely integral straps which are bent back and sealed at 33 to form the loops.

In order to hold the wide end of the skirt or shield 25 at the flared end I5 of the television tube, a specially constructed clamping member 33 is provided (see Figures 1-6). This member 36 is made of stiif flexible plastic material such as polyethylene. This clamping member has the general outline of a circle the size of which is about the same as that of the flange or flared end of the television tube, andthe clamping. member has two interior or inwardly extending annular flanges 3| and 32, one of which (3|) is slightly wider than the other and is adapted to press against the back of the flange or flared end i5 of the tube and the other of which (32) is adapted to extend over the edge portion of the lens id in the front of the tube. The clamping member also includes two exterior or outwardly extending annular flanges :33 and 35 with a groove or channel 34 formed therebetween. The annular flanges (3| and 32 especially) are made of sufiicient thickness and extend at such an angle that they must be forced apart when the clamping member 39 is pressed tightly against the flanged or flared rim I5 of the tube so that when the clamping member 30 is held in place about said flared end I5 the annular flanges 3| and 32 are held tightly against and actually take the form of the flanged portion I5 of the tube as shown in the drawings. The clamping member 33] is held in place by any desired means such as an annular securing member or band (not shown) which is adapted to fit into the groove 34.

In order to make sure that the ring 30 covers every exposed area of the flared flange portion I5 of the tube one of the ends BI] is provided with an integral extension BI of reduced thickness adapted to fit under the arms 3|, 32 of the opposite end 62 as shown in Figure 3.

This end portion 6| may be integrally formed on the end in any desired way. For example the ring 30 may be cut with overlapping endstll and 62 and then the top portionof the overlapping part of the end 60 can be shaved'orcut oif to fit under the arms 3|, 32 of the end 32. Also, a separate piece 6| may be heat sealed to the inside portion of the end'BO. Or the end 6! may be molded from an excess end portion of the end 60 as illustrated in Figures 5 and 6. I

As shown in Figures 5 and 6 the male mold member 66 has a ridge 6'! adapted to fit into the groove formed by the arms 31, 32. The end so of a ring is heated or the mold surfaces 65, 69 are heated and after placing the arms 3|, 32, of the end 60 over the male molding ridge 61, the mold member is forced down on the end 69 to mold the extension 6|.

A preferred method of making the ring of Figure 2 is to injection mold the whole structure in one operation.

A main 40 for electrically connecting the metal back to a point outside the skirt 20 is shown in Figures 1 and 7-9, and comprises an inside con ducting strip 4| adapted to bepressed around and held at the flange of the tube by the ring 30. The strip 4| is connected to the outside bya conducting stud 42 passing'through the skirt 20 andthe outside end has the female portion 43 of a snap fastener secured thereto. The male portion 44 of the snap fastener has an arm 45 to which an outside connecting wire 46 is adapted to be connected as by soldering. The wire 46 can be soldered to the arm 45 while the male snap part 44 is out of contact with any part connected to the heat sensitiveshield on skirt 20.

It will be seen that this invention provides a fool proof ring means for securing an insulating skirt to a metal backed television tube since the securing ring of the invention must always completely cover the outside area of flange of the metal backing. At the same time the ring holds the skirt firmly against the metal backing and also holds the electrical contact element 4| against the metal back.

I claim:

1. A device for electrically shielding a metal backed cathode ray tube having a metal backing section one end of which is adjacent the electrode structure of the tube and the other end of which is flared outwardly to form a rim into which a lens is sealed comprising a skirt of insulating material of substantially the same size and shape as the metal backing, in combination with a flexible, ring-shaped, clamping member of insulating material having a pair of interior annular flanges adapted to straddle the said flared rim of the tube with the end of said skirt held between one of the interior flanges of the clamping member and the flared end of the tube, said clamping member also having a pair of exterior annular flanges forming an exterior channel therebetween, said ring having a gap in its circumference to permit it to be expanded to fit over the flanged rim of said tube, one of the ends formed at the gap containing an integral sleeve of reduced thickness adapted to fit under the interior flanges at the opposed end, and an elastic band adapted to fit into the exterior flange of said ring and hold it tightly about the rim of saidtube and clamp said skirt thereon, a strip of conducting material secured to the inside of said skirt by a conducting element which extends through the said skirt, said strip of con- Y ducting material extending from the latter conducting element toward and adjacent to the edge of said skirt which is held by the ring.

2. A device for electrically shielding a metal backed cathode ray tube having a metal backing section, one end of which is adjacent the electrode structure of the tube and the other end of which is flared outwardly to form a rim into which a lens is sealed comprising a skirt of insulating material of substantially the same size and shape as the metal backing, in combination with a flexible, ring-shaped, clamping member of insulating material having a pair of interior annular flanges adapted to straddle the said flared rim of the tube with the end of said skirt held between one of the interior flanges of the clamping member and the flared end of the tube, said clamping member also having a pair of exterior annular flanges forming an exterior channel therebetween, said ring having a gap in its circumference to permit it to be expanded to fit over the flanged rim of said tube, one of the ends formed at the gap containing an integral sleeve of reduced thickness adapted to fit under the interior flanges at the opposed end, and

an elastic band adapted to flt into the exterior flange of said ring and hold it tightly about the rim of said tube and clamp said skirt thereon.

3. A device for electrically shielding a metal backed cathode ray tube having a metal backing section one end of which is adjacent the electrode structure of the tube and the other end of which is flared outwardly to form a rim into which a lens is sealed comprising a skirt of insulating material of substantially the same size and shape as the metal backing, in combination with -a flexible, ring-shaped, clamping member of insulating material having a pair of interior annular flanges adapted to straddle the said flared rim of the tube with the end of said skirt held between one of the interior flanges of the clamping member and the flared end of the tube, said clamping member also having a pair of exterior annular flanges forming an exterior channel therebetween, said ring having a gap in its circumference to permit it to be expanded to flt over the flanged rim of said tube, one of the ends formed at the gap containing an integral sleeve of reduced thickness adapted to fit under the interior flanges at the opposed end.

4. A device for electrically shielding a metal backed cathode ray tube having a frustoconical metal backing section, the smaller end of which is adjacent the electrode structure of said tube and the larger end of which is flared outwardly to form a rim into which a lens is sealed comprising a skirt of insulating material of substantially the same size and shape as the metal backing, in combination with a flexible, ring-shaped, clamping member of insulating material having a pair of interior annular flanges adapted to straddle the said flared rim of the tube with the end of said skirt held between one of the interior flanges of the clamping member and the flared end of the tube, said ring having a gap in its circumference to permit it to be expanded to fit over the flanged rim of said tube, one of the ends formed at the gap containing an integral sleeve of reduced thickness adapted to fit under the interior flanges at the opposed end.

5. A device for electrically shielding a metal backed cathode ray tube having a metal back ing section one end of which is adjacent the electrode structure of the tube and the other end of which is flared outwardly to form a rim into which a lens is sealed comprising a skirt of insulating material of substantially the same size and shape as the metal backing, in combination with a flexible clamping member of insulating strip material curved upon itself so that the ends thereof abut one another and enclose an area corresponding to the size and shape of the rim of the tube the said clamping member having a substantially uniform cross-sectional shape and having a first pair of flanges extending toward the center portion of the enclosedparea, said first pair of flanges being adapted to straddle the said flared rim of the tube with the end of the skirt clamped between one of the said flanges and an area of the tube adjacent the flared portion thereof, said clamping member having a second pair of flanges extending in approximately opposite directions with respect to said first pair of flanges, said second pair of flanges forming an exterior channel adapted to hold a retaining band for tightening the clamping member about the rim, one of the abutting ends of said clamping member containing an integral sleeve of reduced thickness adapted to fit under the first 7 pair of flanges of the opposite end of the clamping member. 1 RICHARD A. FISCH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Date 4 Number Number Name Date Ehrenberg June 3, 1941 Power Aug. 26', 1941 Bedford Aug. 18, 1942 Patterson, Jr. Nov. 13, 1945 Cain Oct. 14, 1947 Gall .Apr. 27, 1948 Kamin et a1. Jan. 4, 1949 FOREIGN PATENTS Country Date Great Britain Apr. 23, 1940 Great Britain Mar. 31, 1948 

